GB1574364A - Press having an anti-overrun device - Google Patents

Description

PATENT SPECIFICATION

( 11) 1 574 364 ( 21) Application No 4870/77 ( 22) Filed 7 Feb 1977 ( 31) Convention Application No 51/090215 ( 32) Filed 8 Mar 1976 ( 33) Japan (JP) ( 44) Complete Specification Published 3 Sep 1980 ( 51) INT CL 3 F 16 F 9/54 B 30 B 15/14 ( 52) Index at Acceptance F 25 BT B 5 F 1 GX 2 X ( 19) N in ( 54) A PRESS HAVING AN ANTI-OVERRUN DEVICE ( 71) We, AIDA ENGINEERING LIMITED, a Japanese Company, of 2-10 Ohyama-Cho, Sagamihara-Shi, Kanagawa, Japan, do hereby declare the invention for which we pray that a Patent may be granted to use and the method by which it is to be performed to be particularly described in

and by the following statement:-

This invention relates to a press having a device for preventing the slide in a press from descending twice (overrun) in one cycle of a processing operation on a work in such a press.

Hithertofore, attempts have been made for preventing the slide from descending twice, normally referred to as overrun, in a single cycle of processing operation on a work in a press having a friction clutch by an electric interlocking mechanism However, prevention of such overrun of the slide has not been satisfactorily attained because should any electric trouble occur in the electric circuit of the press or any mechanical trouble occur in the rotary cam limit switch associated with the press, overrun of the slide results.

According to the present invention there is provided a press having a slide and a projection extending from the side of a rotary member secured to a crank shaft, and an anti-overrun device including a piston slidably received within a cylinder adapted for mounting on the framework of said press, an oil pressure chamber defined in said cylinder to produce an oil pressure therein as said piston slidably moves within said cylinder and a plurality of orifices formed in the side wall of said oil pressure chamber to be closed in turn as said piston slidably moves within the cylinder, and a pin supported by said piston for movement between an extended position and a retracted position so as to move it into and out of a circular path described by the projection on rotation of the rotary member so that on overrun the projection engages the pin and further movement of the projection is restrained by said slidable movement of the piston within the cylinder.

Reference is now made to the accompanying drawings, in which:Figure 1 is an explanative view showing the angular positions which the crank in a press assumes as the crank rotates; Figure 2 is a fragmentary vertically sectional view taken along substantially the line II II of Figure 3 showing a portion of one preferred embodiment of the anti-overrun device constructed in accordance with the present invention; Figure 3 is a top plan view of Figure 2; Figure 4 is a cross-sectional view taken substantially along the lines IV IV and IV' IV' of Figure 2 respectively; Figure 5 is a schematic view of the pressurised air circuit in the press.

Figure 1 of the accompanying drawings is an explanative view showing the angular positions which the crank in the press assumes as the crank rotates, when the crank is positioned at Point A, the manual push button (not shown) is depressed to actuate the press which in turn shifts the clutch (not shown) to its "ON" position whereupon the crank initiates its rotation.

At this time, however, the clutch tends to shift to its "OFF" position to interrupt the rotation of the crank unless the push button is continuously depressed until the crank rotates to Point B After having passed over Point B, the crank is allowed to continuously rotate to Point C because the clutch is maintained in its "ON" position by an electrical device (not shown) even if the manual depressing force applied to the push button is removed When the crank has rotated to Point C, the rotary cam limit switch (not shown) interlocked with the crank operates to provide a "Clutch Off" signal to operate the brake which in turn c U)Z 1 574 364 stops the rotation of the crank at Point A.

At such a time, reactuation of the crank is prevented even if the push button is maintained in its depressed state, (the crank is prevented from reactuating because the crank is electrically interlocked by a signal from the rotary cam limit switch).

In the above mentioned "Safety-Stroke" mode operation, the crank is maintained at the upper dead point for a predetermined length of time after the crank has completed one rotation for a cycle operation in the press so that a next work to be processed can be fed into the press and thereafter, a cycle of processing operation is performed on the work in the press However, if the rotary cam limit switch and/or brake fail to operate when the crank has reached point C, the crank continues its rotation beyond Point A without stopping there whereby the slide descends twice (overrun) during one complete rotation of the crank This is dangerous to personnel and also can result in damage on the pattern and/or press.

One preferred embodiment of the present invention will now be described referring to Figures 2 through 5 and more particularly, to Figure 2 As shown in Figure 2, a cylinder which is closed at one end is fixedly secured to the framework 6 of the press in a horizontal disposition and receives a piston 1 for slidable movement therein The bottom wall of the cylinder 5 and the inner end of the piston 1 defines an oil pressure chamber D therebetween and the upper wall portion of the cylinder 5 defining the oil pressure chamber D is provided with a plurality of spaced orifices 3 arranged in the displacement direction of the piston 1 The orifices 3 communicate between the oil pressure chamber D and the hollow interior or tank chamber E of an oil tank 4 disposed above the cylinder 5.

The outer end or right-hand end (as seen in Figure 2) of the piston 1 has a hollow block 7 integrally connected thereto and a damper pin 10 (Figure 4) is received in the hollow interior of the block with a bushing 8 (Figure 4) interposed therebetween for slidable movement within the block 7 at right angles to the piston 1 The outer or righthand end of the damper pin 10 (as seen in Figure 4) extends toward a rotary member such as a main gear 14 which is secured to a crank shaft 13 (Figure 4) The other or inner end of the damper pin 10 is connected to the piston rod 12 of a piston 11 a slidable received within an air cylinder 11 which is in turn secured to the hollow block 7.

The rotary member 14 has a stopper pin secured to the outer periphery of the rotary member in opposition to the above mentioned damper pin 10 and the leading end of the stopper pin 15 extends toward the damper pin 10.

The damper pin 10 has a projection at one or the right hand end (as seen in Figure 4) to which a plate 19 is secured and the plate 19 is adapted to move through a slot 18 ' formed in a stopper plate 18 which is in turn secured to the hollow block 7 The stopper plate 18 has a limit switch 17 (the switch is of the lever type) secured thereto, lever 17 a is provided which has a roller 17 b at its leading end to engage the plate 19 so as to operate the limit switch 17 The purpose of the limit switch 17 is to determine whether the damper pin 10 is moving properly or not and the switch 17 is operatively connected to the press actuation push botton (not shown) through an electric circuit.

In Figure 2, it is shown that a spring 2 acts on the piston 1 to urge the piston I and hollow block 7 together in the arrow a direction and the shoulder 18 a formed on the stopper plate 18 abuts against the mating shoulder 5 a on the cylinder 5 to thereby hold the piston 1 in its extended position.

In Figure 2 it is also shown that a cam plate 21 is secured to the stopper plate 18 and a roller 20 b at the leading end of an operation rod 20 a for a limit switch 20 secured to the cylinder 5 The limit switch 20 is designed to shift to its "ON" position so as to break the overall operation electric circuit for the anti-overrun device leading to the power source when the piston 1 has retracted into the cylinder 5 while the device is operating An oil pressure adjusting valve 22 is connected to the cylinder 5 through an oil pressure conduit to limit the oil pressure within the oil pressure chamber D of the cylinder 5 to a predetermined maximum value.

As shown in Figure 2, an oil head gauge 9 is attached to the oil tank 4 and the top of the oil tank 4 is covered by a cover member 23 to prevent splashing of the oil and also to buffer the oil pressure within the oil tank 4.

The oil within the cover member 23 is released through a pipe 24 into the machine body of the press for re-use.

The operation of the anti-overrun device of the invention will now be described.

Referring to Figure 5, in operation, a low air pressure P, acts on the chamber a, of the air cylinder 11 and a high air pressure P, acts on the chamber a, of the cylinder 11.

An electromagnetic valve 25 is provided in the air pressure circuit and designed to be in the "ON" position when the press actuation push button is in its "ON position so as to vent the chamber a, of the air cylinder 11.

The valve 25 is movable to its "OFF" position so as to supply air to the chamber a 2 of the cylinder 11 in response to a signal from the rotary cam limit switch.

When the crank is held at the upper dead point, the electromagnetic valve 25 is in its "OFF" position to supply air to the chamber 1 574 364 a 2 of the cylinder 11 and the air pressure of P 2 minus P, urges the piston 11 a of the cylinder 11 so as to push the outer end of the damper pin 10 out of the hollow block 7.

When the press actuation push button is shifted to its "ON" position, the electromagnetic valve 25 is also shifted to its "ON" position to release the air pressure from the chamber a 2 of the air cylinder 11 and the piston 11 a is urged by the air pressure Pl which normally acts on the chamber a, so as to retract the damper pin 10 into the block 7 At this time, the limit switch 17 is shifted to its "ON" position as the result of the lever 17 a being pushed by the plate 19.

From this time point on, the damper pin 10 continues to maintain its retracted position until the crank reaches Point C' as seen in Figure 1 whereupon the electromagnetic valve 25 is shifted to its "OFF" position in response to a signal from the rotary cam limit switch and piston 11 a is urged by the air pressure of P 2 minus P, so as to push the pin 10 out of the block 7 Under normal operation, the press terminates with the crank positioned at the upper dead point or Point A as seen in Figure 1, the damper pin assumes the position pushed out of the block 7 at an angle to the stopper pin 15 (see Figure 2) and maintains this position until the press actuation push button is depressed for the next cycle of processing operation of the press When the damper pin 10 remains within the block 7 even if the rotary cam limit switch has provided a signal with the crank positioned in Point C', reactuation of the crank is electrically prevented on an account that the limit switch 17 is in its "ON" position.

The damper pin 10 effects one reciprocal movement per stroke movement of the slide and the reciprocal movement of the damper pin 10 is confirmed by the limit switch 17.

When any abnormal condition is found in the movement of the damper pin 10, even if the push button is depressed down the clutch can not be shifted to its 'ONposition and as a result, the crank is prevented from actuating again In order to check the damper pin 10 at the start of operation of the press, the limit switch 17 confirms the pushed-out state of the damper pin 10 to make it possible to energize the main motor (not shown) which rotates the crank.

In a press, when any abnormal condition occurs on the clutch and/or brake, even if the limit switch has provided a clutch "OFF" signal with the crank positioned at Point C as seen in Figure 1, the twicerdescending or overrun of the slide takes place under the conditions as will be described hereinbelow.

( 1) The clutch actuation electromagnetic valve breaks down and as a result, the clutch remains in its "ON" position.

( 2) Even if air pressure for actuating the clutch has been discharged, foreign matters entrapped in the clutch maintain the clutch in its "ON" position.

( 3) Even if the clutch is disengaged, the brake fails to operate.

When the crank continues to rotate under the conditions enumerated hereinabove, the stopper pin 15 strikes against the damper pin 10 to push the piston 1 which in turn discharges the oil within the oil pressure chamber D through the orifices 3 into the tank chamber E of the oil tank E.

At this time, the oil pressure generated within the oil pressure chamber D increases by the resistance offered by the orifices 3 against the flow of the oil and the resistance applied against the piston 1 increases to absorb inertia energy of the press to thereby stop the press.

Since the inertia energy of the flywheel in a press is usually great, it is difficult to absorb the inertic energy of the press including that of the flywheel Out of the abnormal conditions enumerated hereinabove, the abnormal condition ( 3) can be easily eliminated However, under the abnormal conditions ( 1) and ( 2), it is necessary that the value of the reaction force generating by the above-mentioned oil pressure corresponding to the force applied to the pin 10 be increased, the clutch be caused to slip and the force applied to the flywheel be interrupted The overall effective area of the orifices 3 decreases gradually as the orifices 3 are in turn closed when the piston 1 moves within the cylinder 5 in one stroke movement while increasing the reaction force correspondingly At this time, since the clutch slips, the flywheel is decelerated At this time, the main motor is, of course, rendered into its deenergized position by an signal from the limit switch 20.

Operative effects of the preferred embodiment of the present invention will be now described hereinbelow.

( 1) Since the damper pin 10 is operated per stroke movement of the press slide in response to the operation of the press, any extra abnormal condition (overrunning) detection device is not necessary And the operation of the damper pin 10 is checked per stroke movement of the slide and reactuation of the press is prevented whenever an abnormal condition occurs in the operation of the damper pin 10, the anti-overrun device has high safe and reliable characteristics.

( 2) Since the resistance offered by the orifices 3 against the flow of oil produces an oil pressure which acts a damper, any extra oil pressure producing device is not necessary.

1 574 364 ( 3) Since the plurality of orifices 3 are arranged in the stroke movement direction of the piston 1 and the number of the open orifices is gradually reduced as the piston 1 effects its stroke movement, the following advantages can be obtained:

(a) Even if the number of strokes of the slide per minute varies, since a predetermined damping oil pressure generates and the produced oil pressure is maintained, the inertia force can be positively absorbed.

(b) When the causes of the abovementioned twice-descending descend or overrun of the slide are present, and more particularly, when the clutch torque is transmitted to the crank shaft, since the oil pressure generated through the resistance offered by the orifice or orifices against the flow of oil is generally in proportion to a square of the flow velocity of oil, when the clutch torque is transmitted to the crank shaft, if the effective area or cross-section area of the orifice or orifices remains unchanged as the piston 1 effects its stroke movement, the damping action by the orifice or orifices is not effective when the movement speed of the piston 1 decreases.

On the other hand, in order to decrease the flow velocity of oil pressure, when the effective area or cross-section area of the orifice or orifices is reduced, a high oil pressure (peak pressure) generates at the initial stage of the damping action and in consequence, the impact is high According to the present invention, since the gross effective area of the orifices 3 is gradually decreased as the piston 1 effects it stroke movement, even if the piston 1 moves at a relatively low speed, an oil pressure which can overcome the clutch torque generates and in consequence, even when the clutch torque is transmitted to the crank shaft, the press can be positively decelerated whereby the press can be stopped by a low impact and the impact at the initial stage of the damping action is relatively low.

( 4) By the provision of the oil pressure regulation valve in the oil pressure chamber D, generation of any excessive pressure is eliminated when the stroke number of the slide per minute is great.

( 5) Since the damper pin 10 is directly attached to the piston 1 and operated at right angles to the piston 1 the overall size of the anti-overrun device can be reduced to the degree that the device can be mounted within a gear box and can be incorporated in a small size press.

Claims (4)

WHAT WE CLAIM IS:-

1 A press having a slide and a projection extending from the side of a rotary member secured to a crank shaft, and an anti-overrun device including a piston slidably received within a cylinder and mounted on the framework of said press an oil pressure chamber defined in said cylinder to produce an oil pressure therein as said piston slidably moves within said cylinder, and a plurality of orifices formed in the side wall of said oil pressure chamber to be closed in turn as said piston slidably moves within the cylinder, and a pin supported by said piston for movement between an extended position and a retracted position so as to move it into and out of a circular path described by the projection on rotation of the rotary member so that on overrun the projection engages the pin and further movement of the projection is restrained by said slidable movement of the piston within the cylinder.

2 A press according to Claim 1 wherein the pin is supported by said piston for movement at right angles to the movement direction of said piston, the movement of the pin being caused by pneumatically operated means.

3 A press according to Claims 1 or 2 further including a limit switch operatively connected to the piston and cylinder for actuation thereby upon said slidable movement of said piston within the cylinder, the limit switch being arranged for connection to the operating switch of the press so that upon actuation of the limit switch power to the press is switched off.

4 A press according to any preceding claim, further including a further limit switch for actuation by said pin on movement between its extended and retracted positions, the further limit switch being arranged for connection to the operating switch of the press so that when the pin is in its retracted position reactuation of the operating switch is prevented until the pin resides in its extended position.

A press substantially as herein described with reference to and as illustrated in the accompanying drawings.

ERIC POTTER & CLARKSON.

Chartered Patent Agents.

Printed for Hcr Maj Cst V' Sttoionery Offic.

by Cro-don Printing Company L,,naocd Croidon Surrey 1980.

Pubh Ihed hi The Patent Office 25 Son thamplon Buddings.

London WC 2 A l AY tr N huh copice rnay bc obtained